Research on Bending Fatigue Properties of Reinforced Macadam Foundation

Abstract

Existing macadam base structures have poor resistance to bending deformation of pavement. The structural layer is challenged with serious cracking due to the long-term dynamic loads. Despite these issues, however, studies on reinforcement techniques for macadam base structure have been scarce. No reasonable and feasible method on how to improve the bending resistance of flexible base structures (e.g. macadam base structure) and prolong their bending fatigue life has yet been reported. Thus, this study proposed a method for reinforcing macadam base structures with geogrids to strengthen bending performance, anti-fatigue performance and dynamic stability of flexible base structures under different loading levels. The reinforced macadam base structure was investigated through a laboratory test of flexural-tensile strength and a three-point fatigue bending test. A cyclic loading test of reinforced and non-reinforced girder specimens was carried out under five stress levels. The effect of such a new reinforcement method in improving the bending fatigue properties of macadam base structures was analyzed by comparing the yield curves and fatigue lives of reinforced and non-reinforced specimens under different loading levels. Results demonstrate that the non-reinforced macadam base has poor bending resistance. The yield curve and fatigue life of non-reinforced specimens attenuated quickly as it approached the ultimate loading level. Non-reinforced specimens have low-cycle fatigue failures when the loads reach the 0.8 stress level and the ultimate displacement at failure is relatively small, accompanied by obvious failure surface. After geogrids are added, the fatigue life of specimens improved significantly. The yield curve shows no significant attenuation at a high loading level. The reinforced specimens can still maintain high-cycle fatigue failure under the 0.8 stress level and avoid the occurrence of low-cycle fatigue failures. Moreover, reinforced specimens can inhibit transmission of reflection cracks at midspan of cement-stabilized macadam base, delay the propagation of oblique shearing fractures close to the support, and strengthen the dynamic stability and durability of pavement structure with a macadam base. The conclusions of this study provide theoretical references to practical engineering applications of such new reinforcement technology for macadam bases.